Skip `{% generation %}` and `{% endgeneration %}` template handling (#3204)

* Add `.DS_Store` file to `.gitignore`

* Skip `{% generation %}` and `{% endgeneration %}`

Custom syntax within the chat template for the Phi4 Reasoning models
e.g. https://huggingface.co/microsoft/Phi-4-reasoning-plus, which is
AFAIK not handled natively yet, so skipping for now

* Update explanation on `{% generation %}` and `{% endgeneration %}` removal

* Revert "Add `.DS_Store` file to `.gitignore`"

This reverts commit d64d6d2f7f5283b74f1c9aa906d6e68e37edfb48.